The need to provide environmentally correct and cost effective solutions for the refuse generated in the Unites States became apparent in the late 1960's. At that time, refuse disposal was mainly by land filling and to a lesser extent incineration. That situation changed as landfill space became recognized as a finite resource and that refuse could be used as a fuel source which could displace other, more costly, fuel sources in the generation of process steam and electricity. Refuse-to-energy plants became a common source of energy.
A common refuse-to-energy facility, generally indicated by reference numeral 2, is shown in FIGS. 1-2. In operation, a crane or a front end loader, not shown, picks up a quantity of refuse from a refuse storage area and deposits it into charging hopper 4. Charging hopper 4 has a large plan area to facilitate this operation and acts as a funnel to feed the refuse to feed chute 6. Refuse travels down feed chute 6 by gravity until it reaches ram table 8 at the bottom of feed chute 6. Ram feeder 10 pushes refuse from ram table 8 horizontally onto furnace grate system 12 for incineration in combustion zone 14 of furnace 16. As refuse is being burned on grate system 12, flames and intense heat are given off. The heat given off from the burning of refuse in combustion zone 14 is recovered by water carrying boiler tubes 20 which line the walls 18 of furnace 16. Boiler tubes 20 are connected to adjacent boiler tubes by tube joining members 22.
A prior art reciprocating grate system 12 is illustrated in detail in FIG. 3. Grate system 12 is a forward moving reciprocating-type with rows of grate blocks inclined at an angle from the horizontal, e.g., 18.degree., as shown in FIGS. 1 and 2. The grate blocks are grouped into rows perpendicular to the direction of refuse flow. The rows of the grate blocks consist of alternating rows of stationary grate blocks 24 and reciprocating grate blocks 26. Each row of grate blocks overlaps the row ahead of it to provide the grate system surface.
Stationary grate block rows 24 are attached to supports 28. The bottom of supports 28 are affixed to a table 30 which forms a part of the fixed undergrate structure 32. Movable grate block rows 26 are supported by and attached to a common linearly movable carriage 34, via supports 33. Attachment of grate blocks 24 and 26 to supports 28 and 33 is made at the back part of the grate blocks which is located below the prior overlapping block.
Forward and rearward guide units 36a and 36b guide carriage 34 for reciprocatory motion with respect to fixed undergrate structure 32. Each guide unit 36 includes a ramp 38 fixedly mounted to fixed undergrate structure 32, and a wheel 40 mounted to carriage 34. Each wheel 40 is attached to carriage 34 via carriage mounting plate 42 for rotation about an axis perpendicular to the direction of refuse flow. Each wheel 40 includes an axle and a greased bearing arrangement, and is supported by a respective ramp 38 to permit the reciprocating motion of carriage 34 and reciprocating grate blocks 26. Further, supports 33 extend through, and travel within, longitudinal slots located in table 30 during the reciprocating motion of reciprocating grate blocks 26.
A cylinder actuator 44 is attached at one end 46 to fixed undergrate substructure 32 and to movable carriage 34 at the other end 48. Cylinder actuator 44 provides the necessary force to reciprocate carriage 34 and movable rows of grate blocks 26 with respect to fixed undergrate substructure 32 and stationary rows of grate blocks 24. In operation, refuse is pushed onto the grate surface and the movable rows of grate blocks 26 push refuse along the grate surface at a speed dictated by cylinder actuator 44. Air is forced through air holes in fixed table 30 and through holes in the front edge of grate blocks 24 and 26, to control the combustion of the refuse on the grate.
However, there are many potential areas of failure which exist in this "wheel and ramp guide arrangement". First, trash siftings can fall down between the grate block rows and through the air holes and slots in table 30. These trash siftings can fall on one or more ramps 38 and act as a chock to interfere with the ability of wheels 40 to properly roll therealong. Even the binding of one wheel 40 has been known to cause misalignment of the grate blocks and damage the entire grating system 12.
Further, the wheel and ramp guide arrangement includes wheel bearings and axles. The bearings and axles can be expensive as they must be capable to withstand high temperatures for a prolonged period of time and also withstand high temperature differentials when the unit is being brought on and off-line. Additionally, the wheel bearings require periodic greasing. Greasing the wheel bearings is time consuming and requires the plant to be brought off-line because wheels 40 cannot be accessed while the plant is operating. Further, the grease itself can be expensive as it must be specially formulated to withstand the high temperatures and high temperature differentials around the grate.
The wheel and ramp guide arrangement may also be deficient as wheels 40 do not laterally restrain the movement of the carriage 34. Therefore, the grate system requires special lateral side plate restraints to inhibit significant lateral misalignment. However, these plate restraints wear out over time and need to be periodically replaced. As they are not easily accessible, they are expensive to replace. Further, if a side plate restraint is excessively worn and ceases to effectively restrain lateral movement of the carriage, misalignment of the grate blocks and damage the entire grating system 12 will likely occur.
Additionally, the wheel and ramp guide arrangement may also be deficient because it does not include levelling devices. Tolerances and warping of carriage 34 and fixed undergrate structure 32 make it highly unlikely that all the ramp surfaces will be level with respect to each other and level with respect to their respective wheel. This increases the likelihood that some wheels and ramps will wear faster and less evenly than the others, causing uneven wear of the wheels and ramps. When the wheel and ramp surfaces wear unevenly, the possibility of carriage misalignment significantly increases.
In another prior art guide arrangement for reciprocating grate systems, the movable carriage and the fixed undergrate structure are each provided with a flat slide surface. The flat slide surfaces interface to permit the reciprocating motion of the carriage and reciprocating grate blocks with respect to the fixed grate substructure and the stationary grate blocks. U.S. Pat. Nos. 3,651,770 and 3,871,287 illustrate different embodiments of such a "slide surface guide arrangement". However, this flat slide surface guide arrangement also has many deficiencies.
First, the flat slide surfaces do not laterally restrain the movement of the carriage. The system thus requires special lateral side plate restraints to inhibit significant lateral misalignment. As previously described, these plate restraints wear out over time, need to be periodically replaced at a high cost. Further, worn plate restraints can potentially cause grate block misalignment.
Additionally, this fiat slide surface guide arrangement is also deficient because it is highly susceptible to uneven wear of the slide surface members. As the guide arrangement does not include levelling devices, some slide surface members will likely wear faster and less evenly than others. As the surface members wear unevenly, the possibility of carriage misalignment increases. Further, the slide surface members do not appear to easily replaceable. The replacement of the slide surface members would therefore apparently include significant manhours.
Therefore, it would be desirable to have a guide system for a reciprocating grate system that would be able to resist the temperatures conditions found in the grating area. Further, it would be desirable to have a guide system for a reciprocating grate system which eliminates the need for wheels, axles, bearings, and side plate restraints, and the aforementioned disadvantages associated therewith. In addition, it would be desirable to have a guide system for a reciprocating grate system which can compensate for tolerances and warping in the carriage and in the fixed undergrate structure to assure even wear on the guide units.